The presence of amorphous phosphate crystals (calcium and magnesium phosphate) is very common and generally has little clinical significance. They are found in urine with a pH above 6.5. The formation of calcium phosphate crystals can be caused by a combination of factors including decreased urine volume, urine alkalinization (increased pH), or a diet rich in calcium (dairy products). They are also found in individuals with calcium levels that are too high following prolonged immobilization, overactive parathyroid glands or bone metastases, etc.
In individuals with kidney stones, the repeated presence of calcium phosphate crystals could indicate the probable nature of the stone. It should be noted, however, that most patients with calcium and magnesium phosphate crystals will never form stones.